The present invention relates to a mechanical system that modulates airflow in an aircraft inlet diffuser that is used in conjunction with an aircraft engine that integrates both a center turbine engine and a high Mach engine such as a constant volume combustor (CVC) arrangement or ramjet arrangement with intakes formed co-centrically about the turbine. The modulation system uses an articulating cone. When in a retracted position the articulating cone allows the aircraft to operate in low speed mode as only the turbo jet receives airflow. At its widest expanse, the articulating cone completely covers the turbo jet circular intake face, precluding operation of the turbine engine.